All about Metrics

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Where did this metrics string come from - this metrics.http.requests.count?

... lines 1 - 8
class MainControllerTest extends WebTestCase
{
... lines 11 - 12
public function testGetGitHubOrganization()
{
... lines 15 - 16
$blackfireConfig = (new Configuration())
->assert('metrics.http.requests.count == 1');
... lines 19 - 26
}
}

There are two things I want to say about this. First, Blackfire stores tons of raw data about your profile in little "categories" called metrics. More on that soon. And second, inside the assert() call, you're using a special "expression" language that's similar to JavaScript. It's technically Symfony's ExpressionLanguage if you want to read more. Behind-the-scenes, metrics is probably some object... and we're referencing an http property, then a requests... property then a count property & then we're comparing that to 1.

What Metrics are Available

Ok, cool. So... how the heck did I know to use this exact string to get the HTTP call count? This goes back to the Blackfire timeline. On the profile, click the timeline link.

When we talked about the timeline earlier, we talked about how, on the left side, there are these "timeline" metrics. At that point, these were just a nice way to add color to different sections of the timeline.

But now we understand that there is a lot more power behind this info: this shows us all the pieces of data we can use in our tests... and in other places that we'll talk about soon.

For example, there's a metric called symfony.events.count which equals seven. You could use that in a metric if, for some reason, you wanted to assert that a certain number of events were dispatched. If I needed to do an assertion about the number of HTTP requests, I would probably search the metrics for http. Apparently there are two... and if you looked closer, you'd find that http.requests is perfect. Most of these metrics have data about multiple dimensions: we can say http.requests.count to get the actual number or http.requests.memory to get how much memory they used.

In the test system, we start with metrics. then use anything we find here.

Fixing the Performance Bug

We now have a performance bug in our application that we've proven with a test. And at this point, the actual way we fix that bug is not as important: all we care about is that we can change some code and get this test to pass.

The logic for the API calls lives in src/GitHub/GitHubApiHelper.php: it has two public function and each makes one API request:

... lines 1 - 6
class GitHubApiHelper
{
... lines 9 - 15
public function getOrganizationInfo(string $organization): GitHubOrganization
{
$response = $this->httpClient->request('GET', 'https://api.github.com/orgs/'.$organization);
... lines 19 - 25
}
... lines 27 - 30
public function getOrganizationRepositories(string $organization): array
{
$response = $this->httpClient->request('GET', sprintf('https://api.github.com/orgs/%s/repos', $organization));
... lines 34 - 46
}
}

How can we make this page only make 1 HTTP request? Well, if you looked closely.. Ah! Too close! Ahh. You'd find that you can get all the information you need by only making this second HTTP request. The details aren't important - so let's just jump in.

Add a new property called $githubOrganizations set to an empty array:

... lines 1 - 6
class GitHubApiHelper
{
... lines 9 - 10
private $githubOrganizations = [];
... lines 12 - 66
}

As we loop over the repositories for a specific organization, we will store that organization's info. Add a new variable called $publicRepoCount set to 0:

... lines 1 - 6
class GitHubApiHelper
{
... lines 9 - 10
private $githubOrganizations = [];
... lines 12 - 37
public function getOrganizationRepositories(string $organization): array
{
... lines 40 - 44
$publicRepoCount = 0;
foreach ($data as $repoData) {
... lines 47 - 55
}
... lines 57 - 65
}
}

the number of public repositories an organization has is one of the pieces of data we need.

Then, inside the foreach: if $repoData['private'] === false - that's one of the keys on $repoData - say ++$publicRepoCount:

... lines 1 - 6
class GitHubApiHelper
{
... lines 9 - 10
private $githubOrganizations = [];
... lines 12 - 37
public function getOrganizationRepositories(string $organization): array
{
... lines 40 - 44
$publicRepoCount = 0;
foreach ($data as $repoData) {
... lines 47 - 52
if ($repoData['private'] === false) {
++$publicRepoCount;
}
}
... lines 57 - 65
}
}

So, as we're looping over the repositories, we're counting how many are public.

Finally, at the bottom, if not isset($this->githubOrganizations[$organization]), then $this->githubOrganizations[$organization] = new GitHubOrganization():

... lines 1 - 6
class GitHubApiHelper
{
... lines 9 - 10
private $githubOrganizations = [];
... lines 12 - 37
public function getOrganizationRepositories(string $organization): array
{
... lines 40 - 44
$publicRepoCount = 0;
foreach ($data as $repoData) {
... lines 47 - 52
if ($repoData['private'] === false) {
++$publicRepoCount;
}
}
if (!isset($this->githubOrganizations[$organization])) {
$this->githubOrganizations[$organization] = new GitHubOrganization(
... lines 60 - 61
);
}
... lines 64 - 65
}
}

This needs two arguments. The first is the organization name. We can probably use the $organization argument... or you can use $data[0] - to get the first repository - then ['owner']['login']. For the second argument, pass $publicRepoCount:

... lines 1 - 6
class GitHubApiHelper
{
... lines 9 - 10
private $githubOrganizations = [];
... lines 12 - 37
public function getOrganizationRepositories(string $organization): array
{
... lines 40 - 44
$publicRepoCount = 0;
foreach ($data as $repoData) {
... lines 47 - 52
if ($repoData['private'] === false) {
++$publicRepoCount;
}
}
if (!isset($this->githubOrganizations[$organization])) {
$this->githubOrganizations[$organization] = new GitHubOrganization(
$data[0]['owner']['login'],
$publicRepoCount
);
}
... lines 64 - 65
}
}

Now, each time we call this method, we capture the organization's information and store it on this property. So if we call this method first and then the other method... we could cheat and return the GitHubOrganization object that's stored on the property. It's property caching!

Check it out: if isset($this->githubOrganizations[$organization]) then return that immediately without doing any work:

... lines 1 - 6
class GitHubApiHelper
{
... lines 9 - 17
public function getOrganizationInfo(string $organization): GitHubOrganization
{
// optimization in case getOrganizationRepositories is called first
if (isset($this->githubOrganizations[$organization])) {
return $this->githubOrganizations[$organization];
}
... lines 24 - 32
}
... lines 34 - 66
}

So... are we calling these two methods in the "correct" order to get this to work? Check out the controller:

... lines 1 - 16
class MainController extends AbstractController
{
... lines 19 - 54
public function gitHubOrganizationInfo(GitHubApiHelper $apiHelper)
{
... line 57
$organization = $apiHelper->getOrganizationInfo($organizationName);
$repositories = $apiHelper->getOrganizationRepositories($organizationName);
... lines 60 - 64
}
... lines 66 - 120
}

Nope! Swap these two lines so the first call will set up the caching for the second:

... lines 1 - 16
class MainController extends AbstractController
{
... lines 19 - 54
public function gitHubOrganizationInfo(GitHubApiHelper $apiHelper)
{
... line 57
$repositories = $apiHelper->getOrganizationRepositories($organizationName);
$organization = $apiHelper->getOrganizationInfo($organizationName);
... lines 60 - 64
}
... lines 66 - 120
}

Phew! Let's see if that helps. It was a complicated fix... but thanks to our test, we will know for sure if it worked. Go!

php bin/phpunit tests/Controller/MainControlerTest.php

They pass! This proves that we reduced the HTTP calls from two to one.

Typos in Metrics

What I love about the metrics system is that there are many to choose from. What I don't love is that you need to manually look up everything that's available. Fortunately, if you make a typo - the error is great. Change count to vount:

... lines 1 - 8
class MainControllerTest extends WebTestCase
{
... lines 11 - 12
public function testGetGitHubOrganization()
{
... lines 15 - 16
$blackfireConfig = (new Configuration())
->assert('metrics.http.requests.vount == 1');
... lines 19 - 26
}
}

And re-run the test:

php bin/phpunit tests/Controller/MainControlerTest.php

An error occurred when profiling the test

And when we follow the profile link... check out that error!

The following assertions are not valid... Property "vount" does not exist, available ones are:

... and it lists all the properties. That's super friendly. Fix the typo:

... lines 1 - 8
class MainControllerTest extends WebTestCase
{
... lines 11 - 12
public function testGetGitHubOrganization()
{
... lines 15 - 16
$blackfireConfig = (new Configuration())
->assert('metrics.http.requests.count == 1');
... lines 19 - 26
}
}

Organizing Blackfire Assertions into Separate Test Cases

The one downside to adding Blackfire assertions in your tests is that they do slow things down because instrumentation happens and we need to wait for Blackfire to create the profile.

Because of that, as a best practice, we usually like to isolate our performance tests from our normal tests. Check it out: copy the test method name, paste it below, and call it testGetGitHubOrganizationBlackfireHttpRequests():

... lines 1 - 8
class MainControllerTest extends WebTestCase
{
... lines 11 - 28
public function testGetGitHubOrganizationBlackfireHttpRequests()
{
... lines 31 - 38
}
}

And... copy the contents of the original method and paste here. Now... we only need to create the $client, create $blackfireConfig and, inside assertBlackfire(), just make the request:

... lines 1 - 8
class MainControllerTest extends WebTestCase
{
... lines 11 - 28
public function testGetGitHubOrganizationBlackfireHttpRequests()
{
$client = static::createClient();
$blackfireConfig = (new Configuration())
->assert('metrics.http.requests.count == 1');
$this->assertBlackfire($blackfireConfig, function() use ($client) {
$client->request('GET', '/api/github-organization');
});
}
}

Back in the original method, we can simplify... in fact we can go all the way back to the way it was before: create the client, make the request, assert something:

... lines 1 - 8
class MainControllerTest extends WebTestCase
{
... lines 11 - 12
public function testGetGitHubOrganization()
{
$client = static::createClient();
$client->request('GET', '/api/github-organization');
$this->assertResponseIsSuccessful();
$data = json_decode($client->getResponse()->getContent(), true);
$this->assertArrayHasKey('organization', $data);
}
... lines 23 - 34
}

Why is this useful? Because now we can skip the Blackfire tests if we're just trying to get something to work. How? Above the performance test, add @group blackfire:

... lines 1 - 8
class MainControllerTest extends WebTestCase
{
... lines 11 - 23
/**
* @group blackfire
... line 26
*/
public function testGetGitHubOrganizationBlackfireHttpRequests()
{
... lines 30 - 37
}
}

Thanks to that, we can add --exclude-group=blackfire to avoid the Blackfire tests:

php bin/phpunit tests/Controller/MainControlerTest.php --exclude-group=blackfire

Yep! Just one test, two assertions. Another nice detail is to add @requires extension blackfire:

... lines 1 - 8
class MainControllerTest extends WebTestCase
{
... lines 11 - 23
/**
... line 25
* @requires extension blackfire
*/
public function testGetGitHubOrganizationBlackfireHttpRequests()
{
... lines 30 - 37
}
}

Now, if someone is missing the Blackfire extension, instead of the tests exploding, they'll be marked as skipped.

Don't do Time-Based Assertions

The last thing I want to mention about assertions is this: please, please please avoid time-based assertions. They're the easiest to create - I know. It's super tempting to want to create an assertion that the request should take less than 500 milliseconds. If you do this, you will hate your tests.

Why? Because there's way too much variability in time: the request might run fast enough on one machine, but not fast enough on another. Or your server might just have a bad day... and suddenly your tests are failing. Relying on time makes your tests fragile.

Next, we're going to talk more about metrics and assertions. We know that we can add assertions to profiles that are created inside our tests.

But we an also add global assertions: tests that run any time you create a profile for any page! If you want to make sure that a specific page - or any page - doesn't make more than, I don't know, 10 database queries, you can add an "assertion" for that and see a big failure if you break the rules.

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